The Pain was a member of the COBRA Unit in Metal Gear Solid 3: Snake Eater.
The Pain's main skill is the ability to control hornets and seemingly command them. He is able to do this because he carries a queen hornet in his back pouch, the sound of it's wings attracts hornets and renders them under The Pain's control. He uses them as attacks against Naked Snake, but he is also armed with a tommy gun and several grenades, which seem to be conjured by the hornets.
If players deplete The Pain's stamina rather than health, they get the hornet stripe camo, which allows them to control hornets as The Pain did.
It has been revealed that his given name is Claude, a French name.
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